(laughs) captioning sponsored by cbs this is the "cbs evening news" with scott pelley. >> pelley: good evening. as of today we are down to the final four weeks of the presidential campaign. the focus is narrowing, not just to the nine battleground states but to one in particular-- ohio, which could tip the balance on election night. first the big picture. nationally, the latest gallup poll shows mitt romney leading president obama 49% to 47%. that spread is within the margin of error, so it's essentially a tie. in ohio, new polling today shows this: pollster a.r.g. has romney up by one point, 48% to 47%. but a cnn poll has the president up by four, 51% to 47%. either way, it's an improvement for romney who was falling well behind in ohio until last week's debate. both candidates were in ohio today where this is the last day to register to vote. our campaign 2012 correspondents reason there, too, and we'll go to nancy cordes with the obama campaign. >> reporter: scott, ohio is the grand prize for the obama campaign. they have 120 field offices here, the president has held 17 rallies in